This study will test the hypothesis that hypersensitivity to common allergens is a significant predictor of increased rates of decline in lung function among ever smokers. The proposed study will assess the relation between total serum Immunoglobulin E (IgE) concentration and allergic sensitization, and the level and rate of decline of pulmonary function in adult smokers and never smokers. Decreased pulmonary function has been associated with increased reactivity to environmental aeroallergens. Serum IgE mediated allergy causes eosinophilic inflammation of the small airways, thus total serum IgE level has been studied as a potential marker for developing Chronic Obstructive Pulmonary Disease. This study will utilize data from the Tucson Epidemiological Study of Airway Obstructive Disease. The population in this longitudinal study includes 3805 individuals in Tucson, Arizona, enrolled in 1972, and followed for up to 25 years. The roles of IgE and bronchial hyper responsiveness in the relationship between atopy and rate of decline in pulmonary function measures will be assessed with longitudinal analyses using weighted multiple linear regression analysis, with assessment of interactions with smoking, skin test reactivity, and sex. This research will potentially increase understanding of the disease mechanisms, identify new diagnostic procedures and enhance treatment.